Ultraviolet light-emitting device

ABSTRACT

Disclosed is an ultraviolet light-emitting device. The light-emitting device includes: an n-type contact layer including a GaN layer; a p-type contact layer including an AlGaN or AlInGaN layer; and an active region of multiple quantum well structure positioned between the n-type contact layer and the p-type contact layer. In addition, the active region of multiple quantum well structure includes a GaN or InGaN layer with a thickness less than 2 nm, radiating an ultraviolet ray with a peak wavelength of 340 nm to 360 nm.

TECHNICAL FIELD

The present invention relates to an inorganic semiconductor lightemitting device, and more particularly, to an ultraviolet (UV) lightemitting device that emits ultraviolet having a wavelength which is notmore than 360 nm.

BACKGROUND ART

In general, a gallium nitride based semiconductor has been widely usedfor ultraviolet, a blue/green light emitting diode, or a laser diode, asa light source of a full color display, a traffic light, a generallighting, and an optical communication device. Particularly, an indiumgallium nitride (InGaN) compound semiconductor has increasingly beenhighlighted due to a narrow band gap thereof.

A light emitting device using the gallium nitride based compoundsemiconductor has been utilized in various applications such as a largescale full color flat panel display device, a backlight source, atraffic signal, an indoor lighting, a high density light source, a highresolution output system, optical communication, and the like.

GaN has a band gap energy of about 3.42 eV, which corresponds to opticalenergy having a wavelength of about 365 nm. Thus, the light emittingdevice that uses GaN or InGaN as a well layer, has generally been usedto radiate ultraviolet or blue light having a wavelength which is notless than 365 nm. Meanwhile, in order to provide the light emittingdiode that radiates ultraviolet having a wavelength which is not morethan 365 nm, there is a need to increase a band gap of the well layer,and as a result, the well layer with aluminum (Al) added to GaN or InGaNis used (see Korean Patent Laid Open Publication No. 10-2012-0129449).

Further, a barrier layer or a contact layer includes a higher Al contentthan an AlGaN or AlInGaN well layer so as to have a wider band gap thanthe well layer However, as the Al content increases, the AlGaN orAlInGaN layer should be grown at a higher temperature and lowerpressure. That is, a growth condition thereof becomes strict, and as aresult, it is difficult to form an epi-layer having good crystalquality. Further, as the Al content increases, crystal defects such ascracks or threading dislocations caused by stress are prone to occur inthe epi-layer, and as a result, it is difficult to form the epi-layerhaving good crystal quality.

DISCLOSURE Technical Problem

An object of the present invention is to provide an ultraviolet (UV)light emitting device capable of emitting ultraviolet having awavelength in the range of 340 nm to 360 nm. Another object of thepresent invention is to provide a UV light emitting device in whichcrystal quality of a well layer is improved.

Technical Solution

According to an aspect of the present invention, there is provided alight emitting device including: an n-type contact layer including a GaNlayer; a p-type contact layer including an AlGaN layer or an AlInGaNlayer; and an active region having a multiple quantum well structuredisposed between the n-type contact layer and the p-type contact layer.Further, the active region having the multiple quantum well structureincludes well layers formed of GaN or InGaN having a thickness which isless than 2 nm and emits ultraviolet having a peak wavelength in therange of 340 nm to 360 nm.

The well layers formed of GaN or InGaN are formed to have a thicknesswhich is less than 2 nm, such that a band gap is quantized, therebymaking it possible to radiate ultraviolet having a peak wavelength inthe range of 340 nm to 360 nm. Further, the n-type contact layerincludes the GaN layer, such that the well layers having good crystalquality may be formed, and the well layers formed of GaN or InGaN thatdo not contain Al are used, such that well layers having better crystalquality may be formed.

Meanwhile, the well layers formed of GaN or InGaN may have a thicknesswhich is not less than 1 nm but less than 2 nm. A lower limit of thethickness of the well layers formed of GaN or InGaN is not particularlylimited as long as the well layers formed of GaN or InGaN performs afunction as the well layer, but may be preferably not less than 1 nm forstability of an epi-layer growth process.

Meanwhile, the active region having the multiple quantum well structurefurther includes barrier layers. Here, the barrier layers may contain Aland may be formed of AlInGaN. The barrier layers include In, such that alattice mismatching between the well layers and the barrier layers maybe alleviated.

According to some exemplary embodiments, the well layers and the barrierlayers of the active region having the multiple quantum well structuremay be grown at different growth temperatures. Further, the well layersand the barrier layers may be grown by successively introducing sourcegas of In, Ga, and N into a chamber and intermittently introducingsource gas of Al into the chamber.

According to other exemplary embodiments, the well layers and thebarrier layers of the active region having the multiple quantum wellstructure may be grown at the same growth temperature as each other.

Meanwhile, the light emitting device may further radiate ultraviolethaving a peak wavelength in the range of 360 nm to 400 nm together withthe ultraviolet having the peak wavelength in the range of 340 nm to 360nm.

According to some exemplary embodiments, the p-type contact layer mayinclude a lower AlGaN high concentration doping layer, an upper AlGaNhigh concentration doping layer, and an AlGaN low concentration dopinglayer disposed between the lower AlGaN high concentration doping layerand the upper AlGaN high concentration doping layer. Further, the AlGaNlow concentration doping layer may have a thickness thicker than that ofthe lower and upper AlGaN high concentration doping layers. By adoptingthe low concentration doping layer, mobility of holes is increased,thereby making it possible to improve hole injection efficiency.

The light emitting device may further include: a superlattice layerdisposed between the n-type contact layer and the active region; and anelectron injection layer disposed between the superlattice layer and theactive region. Further, the electron injection layer may have n-typeimpurity doping concentration higher than that of the superlatticelayer.

In addition, the superlattice layer may have a structure in whichInGaN/InGaN is repeatedly laminated, and the electron injection layermay be formed of GaN or InGaN.

Meanwhile, the light emitting device may further include an undoped GaNlayer disposed between the n-type contact layer and the superlatticelayer.

According to a specific exemplary embodiment, epi-layers between then-type contact layer and the active region may be formed of nitridebased semiconductor layers that do not contain the AlGaN layer.

Advantageous Effects

According to the related art, a light emitting device that radiatesultraviolet having a wavelength which is less than 360 nm uses a welllayer containing Al and also has an n-type contact layer formed ofAlGaN. Since the contact layer occupying the most of the thickness ofthe light emitting device except for a substrate is formed of AlGaN,crystal quality of an epi-layer, particularly, the well layer is bad andas a result, it is difficult to improve optical power or light emissionefficiency. On the contrary, according to the present invention, thewell layer is formed of GaN or InGaN and the n-type contact layer isformed of GaN, thereby making it possible to form the well layer havinggood crystal quality. Further, the well layer is formed to have a thinthickness which is less than 2 nm, such that a light emitting devicethat radiates ultraviolet having a peak wavelength in the range of 340nm to 360 nm by the well layer formed of GaN or InGaN may be provided.

DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view illustrating a light emitting deviceaccording to an exemplary embodiment of the present invention;

FIG. 2 is a cross-sectional view illustrating a multiple quantum wellstructure of the light emitting device according to an exemplaryembodiment of the present invention;

FIG. 3 is a TEM photograph of the multiple quantum well structuremanufactured according to an exemplary embodiment of the presentinvention; and

FIG. 4 is a graph illustrating an optical spectrum of a light emittingdevice manufactured according to an exemplary embodiment of the presentinvention.

BEST MODE

Hereinafter, exemplary embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings. Theexemplary embodiments of the present invention to be described below areprovided by way of example so that the idea of the present invention canbe sufficiently transferred to those skilled in the art. Therefore, thepresent invention is not limited to the exemplary embodiments to bedescribed below but may be modified in many different forms. Inaddition, in the accompanying drawings, widths, lengths, thicknesses, orthe like, of components may be exaggerated for convenience. Likereference numerals denote like elements throughout the specification.Meanwhile, in the present specification, the content of a metal element(Al or In) denoted by a percentage denotes a composition of each metalcomponent for a summation of compositions of metal components of agallium nitride based layer by percentage. That is, the content of Al ofthe gallium nitride based layer denoted by AlxInyGazN is calculated by100×x/(x+y+z) and is expressed by %.

FIG. 1 is a cross-sectional view illustrating a light emitting deviceaccording to an exemplary embodiment of the present invention and FIG. 2is an enlarged cross-sectional view illustrating a multiple quantum wellstructure of the light emitting device.

Referring to FIG. 1, the light emitting device includes an n-typecontact layer 27, an active region 39, and a p-type contact layer 43.Further, the light emitting device may include a substrate 21, a nuclearlayer 23, a buffer layer 25, an undoped GaN layer 29, a lowconcentration GaN layer 31, a high concentration GaN layer 33, asuperlattice layer 35, an electron injection layer 37, an electronblocking layer 41, or a delta doped layer 45.

The substrate 21, which is a substrate for growing a gallium nitridebased semiconductor layer, is not particularly limited to a sapphiresubstrate, an SiC substrate, a spinel substrate, a GaN substrate, andthe like, but may be, for example, a patterned sapphire substrate (PSS).

The nuclear layer 23 may be formed of (Al, Ga)N at a low temperature of400 to 600° C. in order to grow the buffer layer 25 on the substrate 21,and may be preferably formed of GaN or AlN. The nuclear layer may beformed to have a thickness of about 25 nm. The buffer layer 25, which isa layer for alleviating a defect occurrence such as dislocation betweenthe substrate 21 and the n-type contact layer 27, is grown at arelatively high temperature. The buffer layer 25 may be formed of, forexample, undoped GaN to have a thickness of about 1.5 μm.

The n-type contact layer 27 is formed of a gallium nitride basedsemiconductor layer to which an n-type impurity, for example, Si isdoped, and may be formed to have a thickness of, for example, about 3μm. The n-type contact layer 27 may include a GaN layer and may beformed of a single layer or multiple layers. For example, the n-typecontact layer 27 may include a lower GaN layer 27 a, an intermediatelayer 27 b, and an upper GaN layer 27 c, as illustrated. Here, theintermediate layer 27 b may be formed of AlInN, or may be formed of amultilayer structure (including a superlattice structure) in which AlInNand GaN are laminated in turns, for example, at about 10 periods. Thelower GaN layer 27 a and the upper GaN layer 27 c may be formed to havethicknesses similar to each other, and may be formed to have thethickness of, for example, about 1.5 μm, respectively. The intermediatelayer 27 b may be formed to have a thickness relatively smaller than thelower and upper GaN layers 27 a and 27 c, and may be formed to have thethickness of about 80 nm. By inserting the intermediate layer 27 b intoan intermediate portion of the n-type contact layer 27, crystal qualityof an epi-layer formed on the n-type contact layer 27, particularly, anactive region 39 may be improved as compared to the case in which asingle GaN layer is successively grown to a thickness of about 3 μm tobe relatively thick. Meanwhile, Si doping concentration doped to then-type contact layer 27 may be in the range of 2×10¹⁸/cm³ to 2×10¹⁹/cm³,and may be more preferably in the range of 1×10¹⁹/cm³ to 2×10¹⁹/cm³.Particularly, an Si impurity may be doped on the lower GaN layer 27 aand the upper GaN layer 27 c at high concentration and may be doped tothe intermediate layer 27 b to the same level as or a lower level thanthe upper GaN layer 27 c, and the impurity may also not be intentionallydoped. Since the impurity is doped to the lower GaN layer 27 a and theupper GaN layer 27 c at the high concentration, a resistive component ofthe n-type contact layer 27 may be decreased. An electrode which is incontact with the n-type contact layer 27 may also be in contact with theupper GaN layer 27 c.

The undoped GaN layer 29 may be formed of GaN to which the impurity isnot intentionally doped, and may be formed to have a thicknessrelatively thinner than that of the upper GaN layer 27 c, for example,80 nm to 300 nm. As the n-type impurity is doped to the n-type contactlayer 27, residual stress occurs in the n-type contact layer 27 andcrystal quality is degraded. As a result, in the case in which anotherepi-layer is grown on the n-type contact layer 27, it is difficult togrow the epi-layer having good crystal quality. However, since theimpurity is not doped to the undoped GaN layer 29, the undoped GaN layer29 acts as a restoring layer of restoring degradation in crystal qualityof the n-type contact layer 27. Therefore, it is preferable to directlyform the undoped GaN layer 29 on the n-type contact layer 27 to be incontact with the n-type contact layer 27. In addition, since the undopedGaN layer 29 has specific resistance relatively higher than that of then-type contact layer 27, electrons introduced into the active layer 39from the n-type contact layer 27 may be evenly dispersed within then-type contact layer 27 before passing through the undoped GaN layer 29.

The low concentration GaN layer 31 is disposed on the undoped GaN layer29 and has n-type impurity doping concentration doped at lowerconcentration than the n-type contact layer 27. The low concentrationGaN layer 31 may have an Si doping concentration in the range of5×10¹⁷/cm³ to 5×10¹⁸/cm³, for example, and may be formed to have athickness relatively thinner than that of the undoped GaN layer 29, forexample, a thickness of 50 nm to 150 nm. Meanwhile, the highconcentration GaN layer 33 is disposed on the low concentration GaNlayer 31 and has higher n-type impurity doping concentration than thelow concentration GaN layer 31. The high concentration GaN layer 33 mayhave Si doping concentration of a level which is substantially similarto the n-type contact layer 27. The high concentration GaN layer 33 mayhave a thickness relatively thinner than that of the low concentrationGaN layer 31, and may be formed to have a thickness of about 30 nm, forexample.

The n-type contact layer 27, the undoped GaN layer 29, the lowconcentration GaN layer 31, and the high concentration GaN layer 33 maybe successively grown by supplying metal source gas into a chamber. Asraw materials of the metal source gas, organic materials such as Al, Ga,and In, for example, TMA, TMG, and/or TMI are used. Meanwhile, as sourcegas of Si, SiH₄ may be used. These layers may be grown at a firsttemperature, for example, 1050° C. to 1150° C.

The superlattice layer 35 is disposed on the high concentration GaNlayer 33. The superlattice layer 35 may be formed by alternatelylaminating gallium nitride based layers having different compositions,for example, a first InGaN layer and a second InGaN layer to a thicknessof, for example, 20 Å, respectively, at about 30 periods. Thesuperlattice layer 35 may be formed of an undoped layer withoutintentionally doping the impurity. Since the superlattice layer 35 isformed of the undoped layer, a leakage current of the light emittingdevice may be decreased.

The electron injection layer 37 has n-type impurity doping concentrationrelatively higher than that of the superlattice layer 35. Further, theelectron injection layer 37 may have the n-type impurity dopingconcentration of substantially the same level as that of the n-typecontact layer 27. For example, the n-type impurity doping concentrationmay be in the range of 1×10¹⁹/cm³ to 5×10¹⁹/cm³, and may be morepreferably in the range of 1×10¹⁹/cm³ to 3×10¹⁹/cm³. As the electroninjection layer 37 is doped at high concentration, electrons aresmoothly injected into the active region 39. The electron injectionlayer 37 may be formed to have a thickness which is similar to orrelatively smaller than that of the high concentration doping layer 33,for example, a thickness of about 20 nm. In addition, the electroninjection layer 37 may be grown at a temperature of about 820 to 850° C.and a pressure of about 300 torr.

The active region 39 is disposed on the electron injection layer 37.FIG. 2 is an enlarged cross-sectional view illustrating the activeregion 39.

Referring to FIG. 2, the active region 39 has a multiple quantum wellstructure including barrier layers 39 b and well layers 39 w which arelaminated alternately with each other. The well layers 39 w radiateultraviolet having a wavelength in the range of 340 nm to 360 nm. Thewell layers 39 w may be formed of InGaN or GaN. Here, the content of Incontained in the well layer 39 w may be very small, and may be, forexample, less than about 2%. The well layers 39 w may be formed to havea thickness which is not less than about 1 nm but less than 2 nm. Sincethe well layers 39 w have the thickness which is less than 2 nm, a widthof a quantized band gap is increased, and may consequently radiateultraviolet having a peak wavelength in the range of 340 to 360 nm byGaN or InGaN. The well layers 39 w may be grown at a temperaturerelatively higher than a growth temperature of well layers of a generalblue light emitting diode, for example, at 800 to 820° C. and about 300torr, and as a result, crystal quality of the well layer may beimproved.

The barrier layers 39 b may be formed of a gallium nitride basedsemiconductor layer having a band gap wider than that of the welllayers, for example, GaN, InGaN, AlGaN, or AlInGaN. Particularly, thebarrier layers 39 b may be formed of AlInGaN, where the barrier layers39 b include In, thereby making it possible to alleviate latticemismatch between the well layer 39 w and the barrier layer 39 b.Further, by increasing the content of Al in the barrier layers 39 b, anenergy band gap difference between the well layer and the barrier layermay be increased, and as a result, the wavelength of the radiated lightmay become shorter.

In addition, the barrier layers 39 b may be grown at a growthtemperature slightly higher than that of the well layer (e.g., about 800to 820° C.), for example, at about 820 to 850° C. and about 300 torr.For example, the barrier layer 39 b may be grown by increasing thetemperature after the well layer 39 w is grown. Here, the barrier layermay be grown by stopping an introduction of source gas of In and Gaintroduced into the chamber after growing the well layer 39 w and againintroducing source gas of In, Ga, and Al after increasing the growthtemperature. Unlike this, the well layers 39 w and the barrier layers 39b may be grown by successively introducing the source gas of In, Ga, andN into the chamber and intermittently introducing the source gas of Alinto the chamber. Here, the introduction of the source gas of Al may bestarted after the growth temperature is increased to the growthtemperature of the barrier layer, and may also be started during aprocess of increasing the temperature. The source gas is successivelyintroduced, thereby making it possible to prevent crystal quality of thewell layer from being degraded during a process of increasing thetemperature.

According to some exemplary embodiments, the barrier layers 39 b may begrown at the same growth temperature as that of the well layers 39 w. Inthis case, the barrier layers 39 b and the well layers 39 w may be grownat the same temperature in the range of 800 to 850 r, for example. Sincethe well layer 39 w and the barrier layer 39 b are grown at the sametemperature, evaporation of In and Al which might occur due to anincrease in the temperature may be prevented, thereby making it possibleto improve interface characteristics between the well layer and thebarrier layer.

Meanwhile, a first barrier layer 39 b 1 which is closest to the electroninjection layer 37 or the n-type contact layer 27 among the barrierlayers 39 b 1, 39 b, and 39 bn may have the content of Al higher thanthat of other barrier layers. For example, the content of Al of thefirst barrier layer 39 b 1 may be higher than that of other barrierlayers 39 b as much as 10% to 20%. For example, in the case in which Alof about 20% is contained in other barrier layers 39 b and 39 bn, Al ofabout 30 to 40% may be contained in the first barrier layer 39 b 1. Thecontent of In contained in the barrier layers 39 b 1, 39 b, and 39 bnmay be not more than about 1%. Particularly, in the case in which thewell layers 39 w are formed of InGaN to radiate ultraviolet having thewavelength of 340 to 360 nm, other barrier layers 39 b and 39 n exceptfor the first barrier layer 39 b 1 may be formed of AlInGaN containingAl of 15 to 25% and In which is not more than 1%, and the first barrierlayer 39 b 1 may be formed of AlInGaN containing Al of 30 to 40% and Inwhich is not more than 1%.

In the light emitting device, the barrier layers are generally formed tohave the same composition as each other. However, according to thepresent exemplary embodiment, the first barrier layer 39 b 1 has thecontent of Al higher than that of other barrier layers 39 b as much as10 to 20%. According to the present invention, the electron injectionlayer 37 or the n-type contact layer 27 is formed of GaN. A band gapdifference between the well layer 39 w and GaN that radiate ultravioletis not relatively large. Therefore, the first barrier layer 39 b 1 isformed to have the band gap relatively higher than that of other barrierlayers 39 b, such that the first barrier layer 39 b 1 may perform afunction of confining carriers within the active region 39.Particularly, in the case in which the barrier layer formed of AlInGaNis used, since movement speed of holes is significantly reduced,overflow probability of electrons may be increased. In this case, asolution for preventing the overflow of electrons by increasing athickness of the electron blocking layer 41 may be considered, but thethickness of the electron blocking layer 41 is restrictively increasedto smoothly inject the holes into the active region. Therefore, byforming the first barrier layer 39 b 1 to have the band gap wider (e.g.,not less than about 0.5 eV) than that of other barrier layers, themovement speed of the electrons is decreased, thereby making it possibleto effectively prevent the overflow of electrons. However, in the casein which the content of Al contained in the first barrier layer 39 b 1is excessively increased to not less than about 20%, the latticemismatching between the first barrier layer 39 b 1 and the electroninjection layer 37, and between the first barrier layer 39 b 1 and thewell layer 39 w is increased, thereby making it possible to degradecrystal quality of the active region 39.

Meanwhile, the first barrier layer preferably has substantially the samethickness (e.g., about 45 Å) as or a thickness thicker than that of theremaining barrier layers except for the final barrier layer which isclosest to the electron blocking layer 41 or the p-type contact layer43. The first barrier layer may have the thickness of, for example, 40to 60 Å, and may have particularly the thickness of about 45 Å.

The active region 39 may be in contact with the electron injection layer37. The barrier layer and the quantum well layer of the active region 39may be formed of the undoped layer to which the impurity is not doped,in order to improve crystal quality of the active region, but theimpurity may also be doped in some or all of the active region in orderto decrease a forward voltage.

Referring to again FIG. 1, the p-type contact layer 43 may be disposedon the active region 39, and the electron blocking layer 41 may bedisposed between the active region 39 and the p-type contact layer 43.The electron blocking layer 41 may be formed of AlGaN or AlInGaN, andmay be particularly preferably formed of AlInGaN in order to alleviatethe lattice mismatching with the active region 39. Here, the electronblocking layer 41 may contain Al of about 36% and In of 3%, for example.The electron blocking layer 41 may be doped with p-type impurity, forexample, Mg, at doping concentration of 5×10¹⁹ to 5×10²⁰/cm³.

The p-type contact layer 43 may include AlGaN layer, and may include,for example, a lower AlGaN high concentration doping layer 43 a, anAlGaN low concentration doping layer 43 b, and an upper AlGaN highconcentration doping layer 43 c. The lower and upper high concentrationdoping layers 43 a and 43 c may be doped with the p-type impurity, forexample, Mg, at doping concentration of 5×10¹⁹ to 2×10²⁰/cm³. The lowconcentration doping layer 43 b has doping concentration relativelylower than that of the lower and upper high concentration doping layers43 a and 43 c, and is disposed between the lower high concentrationdoping layer 43 a and the upper high concentration doping layer 43 c.The low concentration doping layer 43 b may be grown by blocking asupply of source gas (e.g., Cp2Mg) of Mg while being grown. Further, thecontent of impurity may be reduced by using N₂ gas except for H₂ gas ascarrier gas during a process of growing the low concentration dopinglayer 43 b. In addition, the low concentration doping layer 43 b isformed to be relatively thicker than the lower and upper highconcentration doping layers 43 a and 43 c. For example, the lowconcentration doping layer 43 b may be formed to have a thickness ofabout 60 nm, and the lower and upper high concentration doping layers 43a and 43 c may be formed to have a thickness of 10 nm, respectively. Asa result, crystal quality of the p-type contact layer 43 may beimproved, and loss of ultraviolet by the p-type contact layer 43 mayalso be prevented or alleviated by reducing impurity concentration.

Meanwhile, a delta doping layer 45 for reducing ohmic contact resistancemay be disposed on the p-type contact layer 43. The delta doping layer45 is doped with n-type or p-type at high concentration to reduce ohmicresistance between an electrode formed on the delta doping layer 45 andthe p-type contact layer 43. The delta doping layer 45 may be formed tohave a thickness of about 2 to 5 Å.

Meanwhile, a light emitting device having a horizontal structure or alight emitting device having a flip-chip structure may be manufacturedby patterning epi-layers grown on the substrate 21, or a light emittingdevice having a vertical structure may also be manufactured by removingthe substrate 21.

Experimental Example 1

Samples have been manufactured by changing only the thicknesses of thewell layers in a state in which other conditions are under the sameconditions. All of the well layers were formed of InGaN, and the contentof In contained in each well layer was a small quantity which is lessthan about 1%. A sample of Comparative Example 1 was manufacturing bygrowing the well layers for about 8 minutes, respectively, a sample ofExample 1 was manufactured by growing the well layers for 4 minutes,respectively, and a sample of Example 2 was manufactured by growing thewell layers for 3 minutes, respectively. The well layer of the sample ofComparative Example 1 had a thickness of about 3.5 nm.

Peak wavelengths of light radiated from light emitting devices ofComparative Example 1, Example 1, and Example 2 were 362.2 nm, 350.6 nm,and 346.5 nm, respectively, at 50 mA. That is, the light emitting devicehaving the peak wavelength which is less than 360 nm may be provided byreducing the thickness of the well layer formed of InGaN.

Experimental Example 2

Samples have been manufactured by changing the content of Al containedin the barrier layers in a state in which other conditions are under thesame conditions. That is, the samples have been manufactured byincreasing a flow rate of source gas of Al by 30% (Example 2-2), 60%(Example 2-3), and 90% (Example 2-4) as compared to the flow rate of thesource gas of Al at the time of growing the barrier layer of a referencesample (Example 2-1). In the case of the reference sample (Example 2-1),the content of Al contained in most barrier layers was about 20%.

The peak wavelengths of light radiated from the respective samples ofthe Examples 2-1, 2-2, 2-3, and 2-4 were 345.5 nm, 342.9 nm, 342.4 nm,and 341.3 nm, respectively, at 50 mA.

The peak wavelength of the light emitting device may be reduced byincreasing the content of Al contained in the barrier layer even thoughthe thickness of the well layer is uniform.

FIG. 3 is a cross-sectional TEM photograph illustrating a quantum wellstructure of the reference sample (Example 2-1) manufactured accordingto an exemplary embodiment of the present invention, and it may be seenthat the well layer has a thickness of about 1.6 nm and the barrierlayer has a thickness of about 4.7 nm.

Meanwhile, FIG. 4 is a graph illustrating a light emitting spectrum ofthe reference sample (Example 2-1) manufactured according to anexemplary embodiment of the present invention.

Referring to FIG. 4, ultraviolet having a peak wavelength of arelatively long wavelength which is not less than 360 nm together withultraviolet having a peak wavelength of a relatively short wavelengthwhich is less than 360 nm is observed.

The ultraviolet having the short wavelength is determined as lightradiated from the well layer, and the ultraviolet having the longwavelength is determined to be radiated by light excitation from a GaNlayer or an InGaN layer having a band gap narrower than that of the welllayer by the light radiated from the well layer.

That is, according to the exemplary embodiments of the presentinvention, the well layer formed of GaN or InGaN is adopted, but thewell layer has the band gap relatively wider than a bulk band gap ofGaN. Therefore, energy of light radiated from the well layer is higherthan band gap energy of the n-type contact layer 27 or other GaNepi-layers. Therefore, the light radiated from the well layer istraveled to the GaN epi-layers, such that light excitation may occur,and as a result, light corresponding to the band gap of GaN may beradiated from the GaN epi-layers.

1. A light emitting device comprising: an n-type contact layer including a GaN layer; a p-type contact layer including an AlGaN layer or an AlInGaN layer; and an active region having a multiple quantum well structure disposed between the n-type contact layer and the p-type contact layer, wherein the active region includes a well layer including GaN or InGaN, the well layers having a thickness less than 2 nm and radiates ultraviolet light having a peak wavelength in the range of 340 nm to 360 nm.
 2. The light emitting device of claim 1, wherein the well layer of the active region has a thickness not less than 1 nm.
 3. The light emitting device of claim 1, wherein the well layer of the active region is free of aluminum (Al).
 4. The light emitting device of claim 1, wherein the active region further includes barrier layers including AlInGaN.
 5. The light emitting device of claim 4, wherein the well layers and the barrier layers of the active region are grown at different growth temperatures.
 6. The light emitting device of claim 5, wherein the well layers and the barrier layers are grown by successively introducing source gases including In, Ga, and N into a chamber and intermittently introducing source gas including Al into the chamber.
 7. The light emitting device of claim 4, wherein the well layers and the barrier layers of the active region are grown at the same growth temperature as each other.
 8. The light emitting device of claim 1, wherein the ultraviolet light is radiated by the well layer.
 9. The light emitting device of claim 1, wherein additional ultraviolet light having a peak wavelength in the range of 360 nm to 400 nm is further radiated.
 10. The light emitting device of claim 1, wherein the p-type contact layer includes a lower AlGaN high concentration doping layer, an upper AlGaN high concentration doping layer, and an AlGaN low concentration doping layer disposed between the lower AlGaN high concentration doping layer and the upper AlGaN high concentration doping layer.
 11. The light emitting device of claim 10, wherein the AlGaN low concentration doping layer has a thickness greater than that of the lower and upper AlGaN high concentration doping layers.
 12. The light emitting device of claim 1, further comprising: a superlattice layer disposed between the n-type contact layer and the active region; and an electron injection layer disposed between the superlattice layer and the active region, wherein the electron injection layer has n-type impurity doping concentration higher than that of the superlattice layer.
 13. The light emitting device of claim 12, wherein the superlattice layer has a structure in which InGaN/InGaN layers are repeatedly laminated, and the electron injection layer includes GaN or InGaN.
 14. The light emitting device of claim 13, further comprising an undoped GaN layer disposed between the n-type contact layer and the superlattice layer.
 15. The light emitting device of claim 1, further comprising: epi-layers between the n-type contact layer and the active region, the epi-layers including nitride based semiconductor layers except the AlGaN layer.
 16. A light emitting device comprising: a first conductivity typed contact layer free of Al; a second conductivity typed contact layer formed over the first conductivity typed contact layer; and an active region disposed between the first and second conductivity typed contact layers and including well layers and barrier layers that are alternately disposed each other, wherein at least one of the well layers is free of Al and emit ultraviolet light having a peak wavelength less than 360 nm.
 17. The light emitting device of claim 16, wherein the first conductivity typed semiconductor layer includes a GaN layer.
 18. The light emitting device of claim 16, wherein the at least one of the well layers include GaN or InGaN.
 19. The light emitting device of claim 16, wherein the at least one of the well layers have a thickness less than 2 nm.
 20. The light emitting device of claim 16, wherein the barrier layers include GaN, InGaN, AlGaN or AlInGaN. 